The Impact of Substrate Materials to the Design of UWB Modern Antennas ()
1. Introduction
Printed circuit board (PCB) microstrip antennas belong to the family of Modern antennas; a category that undoubtedly remains very useful in multiple engineering areas such as aircraft, missiles, rockets, spacecraft [1]-[3]; not forgetting commercial areas like mobile satellite communications, global positioning system, Radio Frequency Identification (RFID), Worldwide Interoperability for Microwave Access (WIMAX), Radar Applications, Telemedicine Applications, military systems [4]-[12], etc.
A transmitted signal is UWB if the RL absolute bandwidth exceeds 500 MHz [13] or the fractional bandwidth is more than 20% at −10 dB; noting that UWB utilization was authorized by the Federal Communications Commission (FCC) to (3.1 - 10.6) GHz in 2002 [14]. According to [15] [16], printed monopole antennas have many possibilities for UWB performance; thus, the present research focus is put on UWB antennas in theory and practice.
2. UWB Antennas’ State of the Art
Some UWB signals were emitted by Hertz in 1887 [17], but the year 2002 awakened both academic and industrial research attention that is continually paid on UWB antennas [18]-[20]. Designers of monopole antennas look forward to reducing ground planes. According to the surveyed UWB antenna designs together with the history of UWB antennas, the reality is that UWB antennas existed for a couple of centuries ago [21] [22].
Learning from different authors, our aim now is to furthermore improve on bandwidth and radiation gain performance for PCB’s UWB antennas.
3. The Antenna Geometry, Design Methodology and Discussed Results
3.1. Design Structure and Methodology
A three dimensional solver high frequency simulator structure (HFSS) based on FEM [23] is the software tool selected for the present research. The 3D design model is presented in Figure 1(a). The main parts of the model: antenna as a top layer, ground as a bottom layer and the substrate as a keep-out layer were exported from Ansoft HFSS Modeler and manipulated with the conjunction of Auto CAD (Computer Aided Design) and Altium Designer’s Printed Circuit Board environment [24] to produce Figure 1(b), which is useful to manufacture the antenna.
For antenna synthesis, the RL is analyzed by time to time to decide on the necessary bandwidth performance. Analyzed over different substrates, the antenna RL results are two dimensionally exported to Microsoft Excel, as. csv format, later compiled together for comparison purpose. Origin Pro 8 for data analysis and graphing is the software tool utilized to prepare the data for Figure 2.
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(a) (b)
Figure 1. Design Model’s (a) three dimensional view; (b) top view.
On RO3003C substrate material, the antenna does not only present optimal fractional bandwidth and radiation gain as detailed in Table 1, but also, the impedance matching with the input feed line is the most competitive for the pre-set frequency of 3.8 GHz. Therefore, all the results presented from Figures 3-8 relate to the antenna simulation on Rogers (ROO3C) substrate. Thus, for this specific research, the selection decision fell on Rogers RO3003C whose dielectric constant is 3.8.
3.2. The Simulation Results
3.2.1. The RL and Voltage Standing Wave Ratio
According to [25], the RL is the measure of how much of the available power is not delivered to the load. The
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Table 1. Antenna bandwidths and gains with different substrates.
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Figure 3. Optimal RL with rogers (RO3003C) substrate.
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(a) (b)
Figure 6. Radiation power pattern (a) in two dimensional view; (b) in three dimensional view.
reflection coefficient of a totally matched load is zero and its RL is infinity. The comparative RL when the unchanged antenna structure is analyzed over different substrate materials is shown in Figure 2. The optimal RL while the antenna printed over the selected substrate material is shown in Figure 3.
The impedance parameters are measured according to Figure 4; as per the Smith Chart’s measurement in Figure 5, the antenna impedance is perfectly matching with the 50 Ω microstrip feed line.
As for the antenna total efficiency (eT), according to [26], knowing the voltage reflection coefficient at input terminals, Γ, such that
(1)
, the input impedance;
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(a) (b) (c)
Figure 7. Radiation fields’ overlay (a) 25%; (b) 50% overlay; (c) 100%.
, the transmission feed line’s characteristic impedance, equals to 50 Ω in normal conditions.
Mathematically, the antenna radiation efficiency is approximately unity since the antenna is simulated under perfect electric conduction (PEC) boundary. So, the computed total antenna efficiency is approximated to the mismatch efficiency; calculations were made possible by the measured impedance parameters in Figure 4. Both the total efficiency and VSWR are now calculated for a resonance frequency of 3.8 GHz.
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3.2.2. Radiation Results
Figure 6 shows both two and three dimensional radiation patterns while Figure 7 and Figure 8 respectively show the radiation fields overlay and the surface currents distribution.
3.3. Discussions
With the resonance frequency of either 3.8 GHz or 5.1 GHz, observable from the RL in Figure 3, carefully viewing UWB antenna standards [14]-[16], the microstrip monopole antenna presented in this research paper is undoubtedly a high gain Antenna for UWB receivers and transceivers. It is expected to be an excellent candidate array element for base stations’ UWB array antenna; thus, highly boosting the obtained maximum radiation gain of 4.23 dB furthermore, in comparison with [20].
Application side, this UWB antenna is expected to find applications with Airport search radar, microwave relays, satellite down communications, Studio-To-Transmitter Link (STL) Microwave relays as well as satellite up communications, as illustrated in Figure 9, a summary made according to [27].
Excellent results were obtained by analyzing the antenna on Rogers 3003C, more competitive than on either Rogers 3003 or FR-4 (Epoxy); it has been made clear in Table 1. Optimally, the simulation reached to (3.3 - 5.8) GHz, absolute bandwidth, highly exceeding 500 MHz [13]. The calculated fractional bandwidth is 67%, certainly greater than 20% [14]. Radiation results indicate the omni-directional radiation; these are very appreciable parameters for UWB Antennas in general.
4. Conclusions
The pre-set goals to review and present the state of the art in UWB antenna has been successfully strengthened
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Figure 8. Magnitude surface current density.
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Figure 9. The antenna’s applications in the microwave spectrum.
by simulation results, presented here in this research article.
For the well conducted simulation, repeatedly yielding the same results, manufacturing results must certainly match with the simulation results.
We are in the process of manufacturing this antenna; it will then be tested and its measured results will be compared to simulation results. Our antenna prototype will undergo several modifications in order to finally hit the target furthermore.
Acknowledgements
A lot of gratitude is addressed to the Government of People’s Republic of China, to have supported and strengthened engineering research activities in the University of Science and Technology of China (USTC). Many thanks also go to the University of Rwanda, college of Science and Technology (UR, CST) for a couple of valuable supports.
NOTES
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*Corresponding author.